Malawi Cichlids Exhibit Toothed Oral and Pharyngeal Jaws

(A) Schematic drawing (lateral view) of the generalized cichlid cranial skeleton, showing the relative location of the oral jaws (purple) and the pharyngeal jaws of PA7 (blue).

(B) Dorsal view of an alizarin red skeletal preparation of the lower pharyngeal and oral elements of a juvenile D. compressiceps (DC) showing the series of branchial (pharyngeal) arches 1–7 and ceratobrachial elements CB1–5; the white asterisk indicates the toothed pharyngeal jaw. Scale bar represents 500 μm.

(C and D) Lateral views with expression of dlx2 labeling neural crest-derived cells in the pharyngeal arches of M. zebra [MZ] (C) and D. compressiceps [DC] (D). Both cichlids are 4 dpf and to the same scale; scale bar in (D) represents 200 μm. dlx2 expression is observed throughout the arches from the mandibular arch, PA1 (black arrowheads), throughout the pharynx to the most posterior arch, PA7 (white arrowheads). dlx2 expression is also present in neural crest-derived mesenchymal cells that populate the arches (white arrows).

(E and F) Sagittal sections of MZ (5 dpf) showing expression of bmp4 in multiple regions of the developing head and pharynx. bmp4 is expressed throughout the arches in neural crest-derived arch mesenchyme for each pharyngeal arch (PA1–7), including both the mesenchyme and epithelial components of the developing teeth (black arrowheads). (E) The medial sagittal section and (F) lateral sagittal section show the gill-bearing arches (PA3–6). Both (E and F) are to the same scale; scale bar in (E) represents 200 μm.